x*(x-21)=1296

Solution for x*(x-21)=1296 equation:

x(x-21)=1296

We move all terms to the left:

x(x-21)-(1296)=0

We multiply parentheses

x^2-21x-1296=0

a = 1; b = -21; c = -1296;
Δ = b2-4ac
Δ = -212-4·1·(-1296)
Δ = 5625
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{5625}=75$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-21)-75}{2*1}=\frac{-54}{2}
=-27
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+75}{2*1}=\frac{96}{2}
=48
$